diff --git a/modules/apps/29-fee/ibc_middleware.go b/modules/apps/29-fee/ibc_middleware.go
index fc58724acfc..9a1042a57c8 100644
--- a/modules/apps/29-fee/ibc_middleware.go
+++ b/modules/apps/29-fee/ibc_middleware.go
@@ -415,6 +415,7 @@ func (im IBCMiddleware) OnChanUpgradeAck(ctx sdk.Context, portID, channelID, cou
 
 // OnChanUpgradeOpen implements the IBCModule interface
 func (im IBCMiddleware) OnChanUpgradeOpen(ctx sdk.Context, portID, channelID string) {
+	// call underlying app's OnChanUpgradeOpen callback.
 	im.app.OnChanUpgradeOpen(ctx, portID, channelID)
 }